How I could have saved Carlo from HumanKode lots of money

So what was the problem? The issue was that it's super-easy to accidently completely break a WPF control when you're just trying to change it's color. Why? Because if you want to change it, you have to completely override the entire control. So you end up having to copy and paste the code for the entire control, and then change what you need. So to fix the issue for Carlo they had to fetch the right control template code and then put it back in. But really, that's just a bandaid over a much, much more complicated problem.